The goal of this research is to increase our understanding of Pseudomonas aeruginosa infections through the study of P. aeruginosa toxins which we have shown catalyze the ADP-ribosylation of mammalian elongation factor 2 (A1 and A2 toxins). Recent studies suggest that these toxins may be important factors in the pathogenesis of P. aeruginosa infections and that the outcome of such infections may be altered through the use of specific antitoxin. Our plan is as follows: (1) To extend our initial observations on the specificity of EF-2 inactivation of A1 toxin produced in vivo. (2) To determine the role of A1 toxin as a virulence factor of P. aeruginosa by (a) comparing the virulence in appropriate animal models of well characterized strains (clinical isolates) of P. aeruginosa which are A1 plus A2-S- to those that are A1-A2-S- and (b) by constructing isogenic isolates of P. aeruginosa altered in A1 toxinogenecity (A1 tox plus and A1 tox minus) and comparing their virulence in animal models. (3) To determine the ability of specific antitoxin to alter the outcome of P. aeruginosa infections. Animals will be used to compare the efficacy of active and passive immunization with A1 toxoid or purified A1 antitoxin antibodies. The presence and titer of human A1 antitoxin will be measured and correlated to the patients' clinical histories and to the toxin producing capabilities of P. aeruginosa isolates. The results of the proposed study will clarify the role of A toxins in the pathogenesis of P. aeruginosa infections, determine if specific antitoxin is protective as well as provide information as to how we might best achieve this type of immunization.